code: def combine_notes(
      audio_notes, start_times, end_times, velocities, sr=16000
  ):
      """Combine audio from multiple notes into a single audio clip.
  
      Args:
        audio_notes: Array of audio [n_notes, audio_samples].
        start_times: Array of note starts in seconds [n_notes].
        end_times: Array of note ends in seconds [n_notes].
        velocities: Array of velocity values [n_notes].
        sr: Integer, sample rate.
  
      Returns:
        audio_clip: Array of combined audio clip [audio_samples]
      """
      n_notes = len(audio_notes)
      clip_length = end_times.max() + MAX_NOTE_LENGTH
      audio_clip = np.zeros(int(clip_length) * sr)
  
      for t_start, t_end, vel, i in zip(
          start_times, end_times, velocities, range(n_notes)
      ):
          # Generate an amplitude envelope
          t_note_length = t_end - t_start
          envelope = get_envelope(t_note_length)
          length = len(envelope)
          audio_note = audio_notes[i, :length] * envelope
          # Normalize
          audio_note /= audio_note.max()
          audio_note *= vel / MAX_VELOCITY
          # Add to clip buffer
          clip_start = int(t_start * sr)
          clip_end = clip_start + length
          audio_clip[clip_start:clip_end] += audio_note
  
      # Normalize
      audio_clip /= audio_clip.max()
      audio_clip /= 2.0
      return audio_clip
  
file_path: magenta/magenta/models/gansynth/lib/generate_util.py
imports: from magenta.models.gansynth.lib import util
  import note_seq
  import numpy
  from scipy.io import wavfile
label_desc: Use image node_id 6 for calling a global function with example usage: combine_notes(audio_notes, start_times, end_times, velocities, sr) and returns: audio_clip